Electromagnetic coupling devices are used for clutches for driving compressors of automobile air conditioning systems. Japanese Kokai Patent Application No. Hei 4[1992]-262127 discloses an electromagnetic clutch which is suitable for driving an air conditioning compressor. The armature assembly includes an armature support member made of reinforced composite material. A metal armature hub, with splines for engaging a spline compressor input shaft, is molded in the composite armature support member or attached to the armature support member by mechanical fasteners. The armature support member has integral stiffener ribs, three rubber damper holders and an armature stop surface. Rubber dampers with integral metal pins are mounted in the rubber damper holders. An armature is attached to the integral metal pins in the rubber dampers. The rubber dampers bias the armature toward the armature stop surface and allow the armature to move away from the armature stop surface and into contact with a clutch rotor when the electromagnetic coil is energized and the clutch is engaged.
Each time the electromagnetic coil of an electromagnetic clutch is energized to engage the clutch, a bending load is placed on the armature support member. Over a period of time and a substantial number of clutch engagements, the damper holders of the armature support member and the armature stop surface adjacent to the damper holders becomes deformed toward the rotor. The deformation occurs with metal armature support members as well as with reinforced composite armature support members. The deformation of the armature support member decreases the air gap between the armature and the rotor when the power to the electromagnetic coil is discontinued. If the air gap is decreased too much, the armature may contact the rotor when the clutch is disengaged. The contact between the armature and the rotor will tend to transmit torque and drive the compressor. Because the armature is not clamped to the rotor by electromagnetic force, there will be slippage and heat will be generated. Heat can destroy and electromagnetic coupling device. The rubber dampers are particularly susceptible to damage by heat.